1. Technical Field
The present invention relates to a line sensor and an image information reading apparatus.
2. Related Art
There have been solid state imaging devices such as a charge coupled device (CCD) sensor and a complementary metal-oxide semiconductor (CMOS) sensor. A line sensor of the solid state imaging device has been used widely for a scanner, a copier, a facsimile and the like. The solid state imaging device has a plurality of photodiodes which generate charge when exposed to light, and functions as a photoelectric conversion element. The photodiodes are formed in an area (hereinafter, referred to as a “photodiode-formed area”) having one side adjacent to which is provided a charge transfer section such as a CCD. For example, when photo-generated charge is generated at each of the photodiodes, an amount of the photo-generated charge is transferred to the charge transfer section via a transfer gate. The photo-generated charge is transferred by the charge transfer section and then read by a reading section as an image signal.
In a case of a scanner having the line sensor mounted thereon, for example, a plurality of line sensor chips as a semiconductor chip are arranged linearly and used. For the line sensor chips arranged, various techniques have been proposed in order to maintain a resolution and prevent an image from being distorted in a gap between the chips.
There are three techniques, for example, for the plurality of the line sensor chips arranged linearly. A first technique is that in each of the chips an interval between a pixel at an end of the chip and an inner adjacent pixel is smaller than an interval between the remaining intermediate pixels thereof (refer to the section “related art” of a first example of related art, listed below, for example). A second technique is that each chip has an array of pixels arranged at a given constant pitch which is set slightly smaller than a reading pitch determined depending on a resolution standard (refer to the first example of related art, for example).
According to the first example of related art, the interval between the pixel at the end of the chip and the inner adjacent pixel is smaller than the interval between the remaining intermediate pixels, the gap between the chips (hereinafter, referred to as a “chip gap”) with absence of pixel is interpolated to prevent image distortion. However, output of the pixel at the end of the chip disadvantageously becomes uneven. In order to solve this disadvantage, the second technique is proposed in which the pixels are arranged in each chip at the given constant pitch which is set slightly smaller than the reading pitch determined depending on the resolution standard.
A third technique is proposed in which an interval between a light receiving element at an end of the chip and an inner adjacent one thereof is wider than that between the remaining light receiving elements (refer to a second example of related art, listed below, for example). At the chip gap of two adjacent chips a distance between the light receiving elements at each of the ends thereof is longer than that of the remaining light receiving elements in one chip. According to the third technique, it is possible to prevent abrupt occurrence of a pitch discontinuity of the light receiving element due to such a condition.
Japanese Patent No. 3013189 (FIG. 2 and FIG. 4) is the first example of related art.
JP-B-7-79403 is the second example of related art.
In the second technique above, unevenness of output of the pixel at the end of the chip is improved, and the number of the pixels of the whole line sensors is kept as it is. However, the image distortion occurs undesirably at the chip gap.
In addition, according to the third technique, since the abrupt occurrence of the pitch discontinuity of the light receiving element is eliminated, the image distortion is reduced. However, there is a problem that, if the light receiving element at the end of the chip is damaged by mechanical shock in a dicing process, as a result, the image distortion occurs.
An advantageous of the present invention is to provide a line sensor which suppresses the image distortion due to the presence of the chip gap.
A line sensor of a first aspect of the invention includes a plurality of pixels which is arranged linearly, the number of the plurality of pixels including the number depending on a resolution, a first pixel group which is provided to a center portion of the plurality of pixels arranged linearly and has a pixel pitch shorter than a length corresponding to a pixel pitch calculated from the resolution, and a second pixel group which is provided to each of both side portions of the center portion, and has a pixel pitch longer than the length corresponding to the pixel pitch calculated from the resolution.
With this configuration, the line sensor can be achieved which suppresses the image distortion owing to the presence of the chip gap.
In the line sensor of the first aspect of the invention, the number of the plurality of pixels is preferably equal to the number depending on the resolution
With this configuration, the line sensor can be achieved which has a resolution the same as that required.
The line sensor of the first aspect of the invention preferably includes a third pixel group. The third pixel group is provided between the center portion and each of the both side portions, and has a pixel pitch equal to the length corresponding to the pixel pitch calculated from the resolution.
The line sensor of the first aspect of the invention preferably includes a third pixel group. The third pixel group is provided between the center portion and each of the both side portions, and has a pixel pitch shorter than the length corresponding to the pixel pitch calculated from the resolution and longer than a length of the pixel pitch of the center portion.
The line sensor of the first aspect of the invention preferably includes a third pixel group. The third pixel group is provided between the center portion and each of the both side portions, and has a pixel pitch longer than the length corresponding to the pixel pitch calculated from the resolution and shorter than a length of the pixel pitch of the both side portions.
With this configuration, the line sensor can be achieved which further suppresses the image distortion owing to the presence of the chip gap.
A line sensor of a second aspect of the invention includes a plurality of pixels which is arranged linearly, the number of the plurality of pixels including the number depending on a resolution. The plurality of pixels are arranged linearly so that the pixel pitch is gradually increased from a center portion of the pixels arranged toward both end portions thereof.
With this configuration, the line sensor can be achieved which suppresses the image distortion owing to the presence of the chip gap.
In the line sensor of the second aspect of the invention, the pixel pitch is preferably changed continuously from the center portion toward the both end portions so as to be increased gradually.
In the line sensor of the second aspect of the invention, the pixel pitch is preferably changed stepwise from the center portion toward the both end potions so as to be increased gradually.
With these configuration, the line sensor can be achieved which further suppresses the image distortion owing to the presence of the chip gap.
A line sensor of a third aspect of the invention includes a plurality of pixels which is arranged linearly, the number of the plurality of pixels including the number depending on a resolution, a first pixel group which is provided to a center portion of the plurality of pixels arranged linearly and has a pixel pitch longer than a length corresponding to a pixel pitch calculated from the resolution, and a second pixel group which is provided to each of both side portions of the center portion, and has a pixel pitch equal to the length corresponding to the pixel pitch calculated from the resolution.
With this configuration, the line sensor can be achieved which suppresses the image distortion owing to the presence of the chip gap.
The line sensor of the third aspect of the invention preferably includes a third pixel group. The third pixel group which is provided between the center portion and each of the both side portions, and has a pixel pitch shorter than the length corresponding to the pixel pitch calculated from the resolution and longer than a length of the pixel pitch of the center portion.
With this configuration, the line sensor can be achieved which further suppresses the image distortion owing to the presence of the chip gap.
An image information reading apparatus according to one of embodiments of the invention includes the above-described line sensor.
With this configuration, the line sensor can be achieved which suppresses the image distortion owing to the presence of the chip gap.